Weld Penetrations with Mig and Tig

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This is a question comparing weld penetration between Mig and Tig in structural steal.  When properly done does one of these processes produce more consistent penetration in welded structural connection?
Reply:Tig is "cleaner" as in no slag.  The only structure I know of is they tig root passes  and some times the whole pipe for nuke.  As for just welding steel, tig is too slow.  DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Economics is a primary consideration when welding anything.... Unless you are doing it for free.  I don't think there is a slower process than TIG.  It is nice and clean when properly done.  Penetration is minimal compared to high voltage and amperage wire feed processes.   As for quality, there are many levels of welding code requirements.  Often a simple visual inspection is all that is required rather than an additional expense of non-destructive testing.   If you inspect the welds on a piece of furniture such as a kitchen chair or even your car you will find all kinds of welding flaws.  Each welding process is more or less suitable for a given application.  Degree of penetration is only one consideration and in the big scheme of things not as important as people believe.
Reply:I work in a refinery and it seems like all pipes are welded with tig now, alot of it is becaues the use of "chrome" in the steel pipe plus more piping is going to 316 stainless steel because of the sulphur in the oil eats the piping even more when heated. Look at the clothes racks in your local store and you will see most of the welds are tig so there is a nice clean small weld with no cleanup, but a mig would have done just fine but the weld would have been bigger so parts are designed with that in mind...BobBob WrightSalem, Ohio  Birthplace of the Silver & Deming Drillhttp://groups.yahoo.com/group/southbend10k/http://groups.yahoo.com/group/sawking/1999 Miller MM185 w/ Miller 185 Spoolmate spoolgun
Reply:Originally Posted by F40This is a question comparing weld penetration between Mig and Tig in structural steal.  When properly done does one of these processes produce more consistent penetration in welded structural connection?
Reply:I think position also gives TIG the advantage.  I've run both orbital TIG and MIG units that revolve around the pipe or tubing being welded.  The TIG is as consistent as it gets in both contour and penetration, while bead contour and penetration change ever so slightly when the MIG welds in the overhead position.  Regardless of parameters, it molten metal bridging the gap is still fighting gravity and relying on surface tension to be pulled into place, whereas the TIG wire starts in contact with the material, and typically freezes at a faster rate, albeit with typically lower deposition.Of course, if you're in a structural environment with heavy structural steel and time/money/HEAVY penetration is a concern, it's tough to beat a sub-arc setup with runoff tabs.
Reply:As for just welding steel, tig is too slow.
Reply:Originally Posted by pulserFor sure, one area of weakness with MIG is at the start of the weld.  When the MIG arc starts the weld, you get less penetration than you do down the weld a ways, when the arc is well established and the base metal is preheated.  You can try to increase MIG penetration at the start, by pausing for some time, but this just builds up more wire that prevents the arc from effectively melting the base metal.
Reply:Originally Posted by SupeOf course, if you're in a structural environment with heavy structural steel and time/money/HEAVY penetration is a concern, it's tough to beat a sub-arc setup with runoff tabs.